The base is defined as the first appearance of the trilobite Lejopyge laevigata around 500.5 million years ago.
[5] The Guzhangian-Paibian boundary is marked by the first appearance of the trilobite Glyptagnostus reticulatus around 497 million years ago.
[4] The name Guzhangian is derived from Guzhang County, Hunan Province, China.
Two phases of extinction can be traced in the sediments of South China: the first, with a slight decline in species, lasted about 1.8 million years; the second, with a sharper decline in richness, lasted 1.2 million years, more in the Paibian.
[7] From the Guzhangian to Jiangshanian, the oceans experienced a gradual depletion of oxygen, which affected bottom-dwelling inhabitants.